I had bought these because of the convenience of them, however do not find them convenient at all. The bottle itself, isn't big enough to place your hand inside to squeeze all the air out of the liners and I have to place something up in the bottle to do that for me. Also, when I do get to squeeze the air out you have to be extremely careful not to squeeze to much pressure or the liner will slip away from the bottle and the milk will poor over you, your furniture, and even your baby. With a hungry baby in your arms waiting to be fed. You do not want to have to go and prepare another bottle (especially in the middle of the night). This is very annoying and a terrible problem. I thought I was going to enjoy using these bottles however, my experience begs to differ.